1. Field of the Invention
The present invention relates to a backlighting system for a LCD type display. More specifically, the present invention relates to a backlighting system that switches redundant light sources on and off in a manner which maintains the level of brightness at an acceptable level for prolonged periods of time.
2. Description of the Related Art
Display technology is rapidly changing with the advent of better and brighter liquid crystal displays (LCDs). As is known, cathode ray tubes (CRTs) are being rapidly replaced by LCDs due to the size and power advantages that are possible with such arrangements.
Most LCDs use an independent backlighting arrangement that is designed to illuminate the liquid crystal arrangements so that comfortable viewing of the images that are generated, is possible. These backlighting arrangements often used either cold or hot cathode fluorescent lamps that are disposed behind the LCD panels. These lamps can be arranged in a number of ways. For example, they can be disposed in the form of edgelights, formed in serpentine configurations, and/or disposed so as to function as direct backlight systems.
However CRTs exhibit a longer working life than LCDs. The basic reason for this resides in the manner in which the two displays are illuminated. CRTs excite phosphor coatings with an electron gun. The weakest link in the CRT is the filament of the electron gun. This element usually exhibits a meantime-between-failure (MTBF) on the order of 30,000 hours. It should be noted however, that MTBF in the display art (and in this specification) is defined as the mean operational hours required for a display's brightness to drop by half.
On the other hand, even though the LCD glass has a typical MTBF on the order of 40,000 hours, the best cold cathode fluorescent lamps (CCFL) currently available only exhibit a MTBF of 20,000 hours. This of course is markedly shorter than MTBF exhibited by CRT, and without repair/maintenance of the LCDs, the CRT displays usually last 50% longer than the best LCD due to the short effective life of the CCFL.
LCDs therefore have encountered the drawback that, unless the life of the backlighting system can be increased to match that of the LCD glass or at least the MTBF of the CRT, the replacement of the CRT type displays with LCDs on an industrial scale, will be inhibited due to undesirably high maintenance costs and/or business shutdowns induced by the need to replace the backlight elements.